So there! Both have the Image Stabilization (Optical Stabilization or OS for Sigma). So the mark 1 version from Canon vs the Sigma's OS version. How is the sharpness and contrast from Sigma 70-200 f2.8 OS compared to the Canon 70-200 f2.8 IS version one. Is the difference in terms of sharpness and contrast huge or noticeable? AF performance of Sigma I hear is more or less on par with the Canon version, but please correct me if I am wrong. Also, can you AFMA Sigma or other 3rd part lenses on a 5DII/III ? Lastly, if I want to add focal length multiplier which teleconverters would be great for the Sigma glass on the bodies mentioned above. Kenko? Thanks.